/*
 * Copyright � 2002-2011 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System.Collections;
using Spring.Collections;

namespace Spring.Expressions.Processors;

/// <summary>
/// Implementation of the distinct processor.
/// </summary>
/// <author>Aleksandar Seovic</author>
public class DistinctProcessor : ICollectionProcessor
{
    /// <summary>
    /// Returns distinct items from the collection.
    /// </summary>
    /// <param name="source">
    /// The source collection to process.
    /// </param>
    /// <param name="args">
    /// 0: boolean flag specifying whether to include <c>null</c>
    /// in the results or not. Default is false, which means that
    /// <c>null</c> values will not be included in the results.
    /// </param>
    /// <returns>
    /// A collection containing distinct source collection elements.
    /// </returns>
    /// <exception cref="ArgumentException">
    /// If there is more than one argument, or if the single optional argument
    /// is not <b>Boolean</b>.
    /// </exception>
    public object Process(ICollection source, object[] args)
    {
        if (source == null)
        {
            return null;
        }

        bool includeNulls = false;
        if (args.Length == 1)
        {
            if (args[0] is bool)
            {
                includeNulls = (bool) args[0];
            }
            else
            {
                throw new ArgumentException("distinct() processor argument must be a boolean value.");
            }
        }
        else if (args.Length > 1)
        {
            throw new ArgumentException("Only a single argument can be specified for a distinct() processor.");
        }

        HybridSet set = new HybridSet(source);
        if (!includeNulls)
        {
            set.Remove(null);
        }

        return set;
    }
}
